It is conventional to control refrigerant flow through an evaporator coil of a refrigeration system with a thermostatic expansion valve which responds to temperature and pressure sensors in an attempt to efficiently evaporate refrigerant via heat removed from a served space. If the refrigerant evaporates too soon, heat transfer efficiency suffers and the refrigerant becomes superheated. Heat transfer occurs more efficiently into the portion of the evaporator coil where the inner coil surface is wetted by liquid refrigerant, and thus it is desirable that the phase change from liquid to vapor occurs as close as possible to the outlet end of the evaporator coil. If all of the refrigerant has not been evaporated, however, liquid refrigerant may be carried into a suction port of a refrigerant compressor, causing slugging and possible damage to the compressor.
It would thus be desirable, and it is an object of the present invention, to provide new and improved refrigeration apparatus and methods which control where a predetermined change in phase occurs in a heat exchanger coil of the refrigeration system, ie., from a liquid to a vapor state or from a vapor to a liquid state.
It would further be desirable, and it is another object of the present invention, to provide new and improved refrigeration apparatus and methods which control where the change in phase from a liquid to a vapor state occurs in an evaporator coil of a refrigeration system, to provide complete evaporation as close to the outlet of the evaporator coil as possible, to increase efficiency of heat transfer, limit superheat, and reduce the chance of liquid refrigerant being drawn into the refrigerant compressor. It would also be desirable to accomplish this phase change location control without requiring the use of a costly pressure transducer.